In the past, there has been proposed an infrared sensor (infrared sensor module) that includes an infrared sensor chip in which a plurality of pixel portions each including a temperature-sensitive portion formed of a thermopile is disposed in an array on one surface of a silicon substrate, an IC chip that processes signals output from the infrared sensor chip, and a package in which the infrared sensor chip and the IC chip are accommodated (for example, see Japanese Patent Application Laid-open No. 2010-78451).
The package described above includes a package main body on which the infrared sensor chip and the IC chip are mounted to be arranged side-by side, and a package cover that is attached to the package main body so as to surround the infrared sensor chip and the IC chip by the package cover and the package main body. Here, the package cover includes a lens that focuses infrared rays to be detected by the infrared sensor chip. In short, the package cover has a function of transmitting infrared rays to be detected by the infrared sensor chip.
In the infrared sensor chip described above, a thermal infrared detector that includes the temperature-sensitive portion of each of the pixel portions is formed on the one surface side of the silicon substrate and is supported on the silicon substrate. Moreover, the infrared sensor chip has a cavity portion which is formed in the silicon substrate immediately below a part of the thermal infrared detector. Further, in the infrared sensor chip, a hot junction of the thermopile that forms the temperature-sensitive portion is formed in a region of the thermal infrared detector that overlaps the cavity portion, and a cold junction of the thermopile is formed in a region of the thermal infrared detector that does not overlap the cavity portion. Furthermore, in the infrared sensor chip, a MOS transistor of a switching element for pixel selection is provided correspondingly to each pixel portions. The MOS transistors are formed on the one surface side of the silicon substrate.
In the infrared sensor described above, since the infrared sensor chip and the IC chip are accommodated in one package, and the wire between the infrared sensor chip and the IC chip can be shortened, it is possible to reduce the influence of exogenous noise and improve noise tolerance.
However, in this infrared sensor, an offset voltage resulting from heating of the IC chip is included in the output signal (output voltage) of each of the pixel portions of the infrared sensor chip, and an S/N ratio varies among respective pixel portions. In short, the S/N ratio varies in a plane of the infrared sensor chip. Here, since the heat which is transferred from the IC chip to the silicon substrate of the infrared sensor chip through the package main body mainly increases the temperature of the cold junction, this heat becomes a factor that generates a negative offset voltage. On the other hand, since the heat which is transferred from the IC chip to the infrared sensor chip due to heat radiation or heat conduction via a medium (for example, nitrogen gas or the like) inside the package mainly increases the temperature of the hot junction, the heat becomes a factor that generates a positive offset voltage.